linux-kernel - Re: [PATCH v4 3/3] configfs: Add unit tests

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Date:   Tue, 10 Aug 2021 14:50:50 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Bart Van Assche <bvanassche@....org>,
        Christoph Hellwig <hch@....de>
Cc:     Joel Becker <jlbec@...lplan.org>, linux-kernel@...r.kernel.org,
        Bodo Stroesser <bostroesser@...il.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Yanko Kaneti <yaneti@...lera.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v4 3/3] configfs: Add unit tests

On 8/10/21 12:45 PM, Bart Van Assche wrote:
> On 8/10/21 9:50 AM, Christoph Hellwig wrote:
>> On Mon, Aug 09, 2021 at 11:31:23AM -0700, Bart Van Assche wrote:
>>>>> +config CONFIGFS_KUNIT_TEST
>>>>> +    bool "Configfs Kunit test" if !KUNIT_ALL_TESTS
>>>>> +    depends on CONFIGFS_FS && KUNIT=y
>>>>> +    default KUNIT_ALL_TESTS
>>>>
>>>> Why does it depend on KUNIT=y?  What is the issue with a modular KUNIT
>>>> build?
>>>
>>> The unit tests calls do_mount(). do_mount() has not been exported and
>>> hence is not available to kernel modules. Hence the exclusion of KUNIT=m.
>>
>> You should probably document that.  But then again this is another
>> big red flag that this code should live in userspace.
>>
>>>> To me this sounds like userspace would be a better place for these
>>>> kinds of tests.
>>>
>>> Splitting the code that can only be run from inside the kernel (creation
>>> of configfs attributes) and the code that can be run from user space and
>>> making sure that the two run in a coordinated fashion would involve a
>>> significant amount of work. I prefer to keep the current approach.
>>
>> But userspace is the right place to do this kind of pathname
>> based file system I/O.
> 
> Shuah, as selftest maintainer, can you recommend an approach? How about splitting patch 3/3 from this series into a kernel module (the code that creates the configfs test attributes) and user space code (the code that reads and writes the configfs attributes) and adding the user space code in a subdirectory of tools/testing/selftests/?
> 

I am missing a lot of context here. I don't see this series in my inbox
except patch 2/3 which says:

"A common feature of unit testing frameworks is support for sharing a test
configuration across multiple unit tests. Add this functionality to the
KUnit framework. This functionality will be used in the next patch in this
series."

That doesn't tell me much other than what happens that it is a common unit
testing framework without explaining why it should be done this way.

Taking a quick look at the original message on lore - I agree with Christoph
that this code belongs in userspace. I would like to see the division of
kernel userspace.

Why do the unit tests need to call do_mount() - can whatever the unit tests
are currently doing can be done from userspace.

If part of the test code must live in kernel space then kernel test module
approach can be used.

thanks,
-- Shuah